Electrohydraulic control apparatus for anti-lock brake system

ABSTRACT

An anti-locking hydraulic brake system in which the pedal is brought into a variable position during a brake pressure control action. A correcting variable is determined in such a way that any pressure rating in the power chamber is correlated with a position of the power piston, the correlation between the pressure and the position roughly corresponding to the ratio of pressure and position during a noncontrolled braking action.

FIELD OF THE INVENTION

The present invention relates to an electrohydraulic control apparatusfor use in an anti-lock vehicle braking system of the type which isdescribed in GB-A-22 197 402. An improvement upon the apparatus ofGB-A-22 197 402 is illustrated in U.S. Pat. No. 4,892,364. FR-A-26 20991 is also considered as state of the art.

BACKGROUND OF THE INVENTION

It is described in the first-mentioned publication that during a controlaction the power piston of the master cylinder is brought into a definedposition which guarantees that a sufficient volume of pressure fluidremains in the master cylinder so that the vehicle still can be brakedto a sufficient extent in the event of failure of the pumps. The definedposition is referred to by "B" in the publication. In the course of acontrol action, the power piston, and hence the pedal, are brought intoa defined position which is independent of the pedal effort beingbrought to bear by the driver. The relation between the pedal travel andthe brake pressure and, respectively, master cylinder pressure during anon-controlled braking action which is known to the driver is, thus,lost.

U.S. Pat. No. 4,892,364 suggests accomplishing the pedal positioning byvariation of the delivery volume of the pump, and particularly to changethe drive power of the pump motor. It is known from the Frenchspecification to vary the effective output of a pump in an anti locksystem in that, with the drive power of the pump motor remainingconstant, a by-pass between the pressure side and the suction side ofthe pump is opened so that the pump delivers in a circuit, and effectivefluid delivery into the brake circuit does not take place.

SUMMARY OF THE INVENTION

The present invention has as an object to adapt the position of thepower piston and, respectively, of the pedal to be adjusted to themaster cylinder pressure also during a control operation.

It is a further object of the present invention to put at disposalappropriate means for monitoring the power piston travel. The knownapplications provide for a switch which is actuated directly by thepower piston. This arrangement is cumbersome to mount and difficult toadjust. It is therefore proposed to arrange a flowmeter in the brakeline, with the quantity of pressure fluid entering into or exiting fromthe power chamber of the master cylinder being sensed, whereby directconclusions can be drawn in regard to the position of the piston.

Further details of the invention will be explained by the followingdescription of one embodiment.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows an anti-locking control apparatus according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The apparatus is comprised of the following units: a vacuum brake powerbooster 9 which is actuated by the brake pedal 1, a tandem mastercylinder 16, a modulator 2 for the pressure control during theanti-locking control mode, an electronic controller 5 for the processingof sensor signals, and a hydraulic pump 7, 8 which is driven by anelectric motor 6.

In the FIGURE, the system is shown with the brake pedal in the releaseposition. The pressure chambers 10, 15 of the master cylinder areconnected in a known manner to the hydraulic fluid reservoir 3 throughopen central valves, connecting ducts in the interior of the pistons,and annular chambers 13, 14 in the power pistons 11, 12 , bores andhydraulic lines 19, 20.

The two pressure circuits 21, 22 of the master cylinder are connected tothe wheel brakes 27, 28, 29, 30 through electromagnetically actuatableinlet valves 23, 24, 25, 26 switched to open in the basic position whende-energized ("SO valves").

The wheel brakes 27, 28 and 29, 30, switched in parallel, respectively,are associated with the diagonally arranged pressure circuits (brakecircuits) 21, 22. The following designations are selected to denote thearrangement of the vehicle wheels corresponding to the aforementionedbrakes: "VL" for front left, "HR" for rear right, "VR" for front right,"HL" for rear left. The wheel brakes 27, 28, 29, 30 are, furthermore,connected to the reservoir 3 through electromagnetically actuatableoutlet valves 31, 32, 33, 34 which are closed in the basic position,that is to say when de-energized ("SG valves"), via a return line 4. Thevehicle wheels are equipped with inductive sensors S which interact withtoothed discs rotating synchronously with the rotation of the wheels andwhich generate electric signals representative of the rotationalbehavior of the wheels, that is to say, the circumferential wheel speedand changes of that speed. These signals are conveyed to the electroniccontroller 5. The electronic controller processes the sensor signals onthe basis of a control algorithm generating output signals (brakepressure control signals) by which the SO valves and SG valves areswitched in the brake pressure control mode, as a result of which thebrake pressures are decreased, are kept constant or are increased againin the individual wheel cylinders in accordance with the controlalgorithm. For this purpose, the actuating magnets of the SO valves andSG valves are actuated through the outputs of the electronic controller.In the brake pressure control mode, the electric motor 6 of the pumps 7,8 is put into operation. The switching-in signal is supplied to theelectric motor by the electronic controller 5. In the control mode, thepump builds up pressure in the pressure lines 50, 51. These linesrepresent a hydraulic fluid path which is linked to the hydraulic fluidpath of the tandem master cylinder in the form of the pressure lines 21,22. This means that in the control mode, the pressure chambers 10, 15 ofthe tandem master cylinder are pressurized by the pumps.

During operation of the brake in the normal braking mode, the pedaleffort F, assisted by the vacuum within the booster 9, will betransmitted to the master cylinder pistons. The central valves in thepistons close, as a result of which pressure can now build up within thepressure chambers 10, 15 and, thus, in the brake circuits 21, 22, whichpressure is conveyed, through the SO valves 23, 24, 25, 26, to the wheelcylinders. Now, if and when a locking tendency is recognized at one orat a plurality of wheels with the aid of the sensors S and of theelectronic controller 5, then the anti-locking control mode will bestarted. The driving motor 6 of the pumps 7, 8 will be switched in, as aresult of which pressure will be built up in the pressure lines 50, 51which acts, on one hand, through the SO valves, on the wheel cylindersof the wheel brakes and which, on the other hand, pressurizes thepressure chambers of the master cylinder as described above.

In accordance with the control algorithm, further signals from theelectronic controller 5 lead to a switching-over of theelectromagnetically actuatable SO and SG valves.

As a result of the pump pressure within the power chambers 10 and 15,the power pistons 11 and 12 in the FIGURE will move to the right.

The apparatus includes the following in order to achieve, during acontrol action, a fixed relation between the brake pedal position andthe pressure in the master cylinder and the power piston.

The flowmeters 65, 66 are incorporated in the brake lines 17, 18 at theoutlet of the master cylinder. Downstream of the flowmeters, thepressure lines 50, 51 end in the brake lines.

Flowmeters 65, 66 detect both the volume of hydraulic fluid which isconveyed from the power chambers into the brake circuits and the flow ofhydraulic fluid in the opposite direction. An indication of the flowrates therefore permits drawing a direct conclusion on the position ofthe power piston. Signals representative of the flow through flowmeters65, 66 are supplied to electric motor control unit 55.

In addition, pressure sensors 69, 70 detect the pressure within thepower chambers 15, 10. Pressure sensors 69, 70 convert the hydraulicpressure into electric signals which are conveyed over the lines to theelectric motor control unit 55.

Reference numerals 75, 76 represent control algorithms which will becalled volume models in the following.

With the aid of the volume models, the volumetric demand for the powerchambers of the tandem master cylinder is calculated. The deliveryvolumes of the pumps are established such that an arbitrary theoreticalposition of the power pistons and, thus, of the brake pedal is reachedduring the anti-locking control mode. Signals representative of thevolumetric demand of the tandem master cylinder are supplied to theoutput of the electronic controller 5 which are transmitted over theelectric lines to the electric motor control unit 55.

The electric motor 6 is furnished with a sensor 81 for sensing therotation rate of the motor.

The functions of the electric motor control unit comprise switching themotor on and off through a relay, controlling the electric motor and,consequently, the delivery volumes of the pumps in order to achieve thetheoretical positions of the power pistons of the master cylinder and ofthe brake pedal. The functioning of the pumps, the rotation rate of themotor, the pressure in the power chambers, and the supply of asufficient reserve of hydraulic fluid for the master cylinder aremonitored.

The control of the electric motor serves to increase the operatingcomfort of the brake pedal and besides the positioning itself also todefine the positioning speed for the brake pedal. Furthermore, avirtually complete noise absorption can be attained by the control ofthe electric motor.

The apparatus works as follows:

Signals for the volumetric demand for the push rod piston and thefloating piston are furnished during the control mode on the basis ofthe volume models 75, 76 which are stored in the electronic controller.The volumetric demand signals are processed in the electric motorcontrol unit 55 together with the travel sensor signals, the pressuresensor signals and the rate-of-revolutions sensor signals to generateposition signals at the output connected to the electric motor. As aresult, the delivery volumes of the pumps 57, 58 are varied. By thevariation of the delivery volumes, the desired positioning andpositioning speed of the power pistons, in particular of the push-rodpiston, and, thus of the brake pedal, are brought about.

As an alternative of or in addition to the regulation through theelectric motor, the pump valves 61, 62 can be employed which are clockedand which, thus, vary the delivery rate of the pumps in accordance withthe control algorithms stored in the electronic controller.

An exact positioning of the pedal and a comprehensive monitoring of thepumps are achieved by the described system. The delivery volumes of thetwo actuating circuits of the brake system permit individual control.The pedal feeling is improved. The energy consumption is reduced. Astandard tandem master cylinder with a breather hole system can beemployed as a tandem master cylinder.

The effect of the measures described in the embodiment of the presentinvention is that, during a brake pressure control action, a definedrelationship exists between the pedal effort and the pedal travel. Theresult, very easily achieved by the described means, is a determinationof the travels of the power pistons and, thus, of the pedal inparticular, due to the inclusion of flowmeters.

What is claimed:
 1. A system for anti-lock braking control of a vehiclecomprising:a brake pedal; a master cylinder responsive to movement ofsaid brake pedal and having at least one pressure chamber in which fluidpressure varies with brake pedal movement in a predetermined mannerunder normal braking; a plurality of brakes; first sensing meansresponsive to the rotational behavior of a plurality of wheels of thevehicle individually associated with said brakes for developing brakepressure control signals representative of a locking tendency of any ofthe wheels; a pressure fluid reservoir; an auxiliary pressure source;pressure fluid conducting means extending between said pressure fluidreservoir, said brakes, said pressure chamber of said master cylinder,and said auxiliary pressure source for conducting pressure fluid:(a)between said pressure fluid reservoir and said brakes, (b) between saidauxiliary pressure source and said pressure chamber, (c) between saidauxiliary pressure source and said brakes, and (d) between said pressurechamber and said brakes; second sensing means for developing:(a)pressure fluid flow signals representative of the flow of pressure fluidinto and from said pressure chamber of said master cylinder, and (b)pressure fluid pressure signals representative of the pressure ofpressure fluid in said pressure chamber; means for supplying volumetricsignals representative of the volume of pressure fluid required in saidpressure chamber of said master cylinder to position said pedal after alocking tendency has been sensed at a selected position corresponding tosaid selected position of said brake pedal under normal braking; andmeans responsive to:(a) said brake pressure control signals, (b) saidpressure fluid flow signals, (c) said pressure fluid pressure signals,and (d) said volumetric signals for actuating said auxiliary pressuresource and for controlling the passage of pressure fluid through saidpressure fluid conducting means: (a) between said pressure fluidreservoir and said brakes, (b) between said auxiliary pressure sourceand said pressure chamber. (c) between said auxiliary pressure sourceand said brakes, and (d) between said pressure chamber and said brakes.2. A system for anti-lock braking control of a vehicle according toclaim 1 further including second pressure fluid conducting meansextending between said pressure fluid reservoir and said pressurechamber of said master cylinder.
 3. A system for anti-lock brakingcontrol of a vehicle according to claim 1 wherein said master cylinderis a tandem master cylinder and has a second pressure chamber and:(a)said second sensing means develop:(i) pressure fluid flow signalsrepresentative of the flow of pressure fluid into and from both saidpressure chambers of said tandem master cylinder, and (ii) pressurefluid pressure signals representative of the pressure of pressure fluidin both said pressure chambers of said tandem master cylinder, and (b)said means for supplying volumetric signals supply volumetric signalsrepresentative of the volume of pressure fluid required in both saidpressure chambers of said tandem master to position said pedal after alocking tendency has been sensed at a selected position corresponding tosaid selected position of said brake pedal under normal braking.
 4. Asystem for anti-lock braking control of a vehicle according to claim 3wherein said second sensing means include:(a) a first flowmeter in saidpressure fluid conducting means at an outlet from one of said pressurechambers of said tandem master cylinder for developing pressure fluidflow signals representative of the flow of pressure fluid into and fromsaid one pressure chamber, and (b) a second flowmeter in said pressurefluid conducting means at an outlet from the other of said pressurechambers of said tandem master cylinder for developing pressure fluidflow signals representative of the flow of pressure fluid into and fromsaid other pressure chamber.
 5. A system for anti-lock braking controlof a vehicle according to claim 4 wherein said second sensing meansfurther include first and second pressure sensors individuallyresponsive to fluid pressure in said pressure chambers of said tandemmaster cylinder for developing said pressure fluid pressure signals. 6.A system for anti-lock braking control of a vehicle according to claim 5wherein said auxiliary pressure source includes:(a) a motor, (b) pumpmeans driven by said motor and having a pressure end and a suction endfor supplying pressure fluid to said pressure chambers of said tandemmaster cylinder and said brakes, and (c) valve means extending betweensaid pressure end of said pump means and said suction end of said pumpmeans for regulating pressure fluid supplied by said pump means.
 7. Asystem for anti-lock braking control of a vehicle according to claim 5further including a brake power booster disposed between said brakepedal and said tandem master cylinder and coupling said brake pedal tosaid tandem master cylinder.
 8. An anti-locking control apparatus forhydraulic automotive vehicle brake systems, with a master cylinder whichcomprises at least one power piston and one power chamber, with aplurality of wheel cylinders, with a pressure modulator which comprisesthroughflow valves and shut-off valves and which modulates hydraulicpressure in the wheel cylinders during a controlled braking action; withat least one pump connecting with its pressure side to the power chamberand to the pressure modulator, with at least one electronic controllerwhich processes wheel sensor signals to generate position signals forsaid throughflow and shut-off valves of the pressure modulator, with atravel sensor to monitor the movement of said power piston and fordeveloping travel sensor signals, a pressure sensor to monitor thepressure in the power chamber and for developing pressure sensorsignals, with the travel sensor signals and the pressure sensor signalsbeing employed as a correcting variable to control the delivery volumeof the pump, characterized in that the correcting variable is determinedin such a manner that any pressure rating in the power chamber iscorrelated to a position of the power piston, wherein the correlationbetween the pressure rating and the position of the power piston roughlycorresponds to a correlation between the pressure rating and theposition of the power piston during a noncontrolled braking action, withthe proviso that a minimum quantity of pressure fluid remains in thepower chamber of the master cylinder.
 9. An apparatus as claimed inclaim 8, characterized in that brake lines lead away from the powerchamber of the master cylinder and flow sensors, positioned in the brakelines, monitor the quantity of pressure fluid which flows into an fromthe master cylinder.
 10. An apparatus as claimed in claim 8,characterized in that the pressure side of the auxiliary pump isconnected to the suction side by a line which is furnished with a valveelement, wherein said valve element is responsive to the correctingvariable and is an electromagnetically actuatable valve which shuts offin its position of rest and which is switchable by electric signals. 11.An apparatus as claimed in claim 8, characterized in that the pump isdriven by an electric motor, the correcting variable being utilized toclock the electric voltage of the drive motor and, thus, to control thenumber of revolutions.